|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: RE: Filament hum posted by vinnie2 on September 14, 2016 at 13:05:24:
Triode_Kingdom did all the leg work on this using a simple 12v supply off Ebay.
You can no longer find the exact supply but one similar. I did this last year using TK methods and it worked perfect!
Triode_Kingdom Supply Link
--------------------This is the content and basic instructions--------------------
The first thing you have to do is pop the top off the box so you can get at the circuitry. Removing the PC board is a simple matter, once the box is open. Next, ferret out the connections at the four rectifier diodes and determine which leads represent the + and - output. You will then need to add a capacitor across those points, approximately 450uF / 200VDC.
Now, the next time you plug in the supply, it won't work. You'll discover that a small resistor (0.1 or maybe 1 ohm) located at the edge of the board has opened. That occurs because this is a fusible resistor, and the surge created by charging the new capacitor is too much. Replace the resistor with a 5 ohm, 5-10 watt part.
The next issue to deal with is the output frequency. 25 KHz is too low for audio work. The board contains a small toroidal transformer, and that needs to be modified. Remove the transformer from the board and you'll see it has two separate windings, about five or six turns each. Cut one end of each winding loose and unwrap all but one turn of each. Resolder the loose end of each winding. The next time you fire up the supply, it will output a 12V squarewave at approximately 60-65 KHz.
The last thing you'll need to do to use the supply is to add a dropping resistor at its output. The supply outputs 12V, so for a 211 drawing 3.25A, you'll need approximately 0.6 ohms. I use two 0.33 ohm resistors, one in each leg of the filament. I should add that I much prefer this approach to any sort of constant voltage regulation, or to modifying the turns ratio of the power supply's output transformer (not the same transformer mentioned previously). At the very least, the dropping resistors help to mediate the inrush current when the tube is cold. I mount the resistors directly to the filament posts of the 211 socket.
To use the supply, you'll need to mount the PS circuit board in a larger case. It won't fit in the original plastic container with the addition of the larger resistor and the filter cap. Make sure the PC board is well insulated from anything metal. The input circuit (oscillator transistors, diodes, filter cap, and toroid) are electrically connected to the AC line. In fact, only the two output leads (driven by the conventional output transformer) are isolated.
The Ebay link is the supply I used, just search for "12v halogen supply
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- RE: Ultrasonic Link - deafbykhorns 10:20:56 09/15/16 (1)
- RE: Ultrasonic Link - vinnie2 12:51:13 09/15/16 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
